Petroleum is a complex mixture of paraffinic, cycloparaffinic, and aromatic hydrocarbons containing components that range in character from free-flowing liquids to waxy solids and tars. Generally, the solid components are termed paraffinic if their primary composition is aliphatic, and asphaltenic if the primary composition is aromatic. Both asphaltenes and paraffins are commonly found associated with petroleum.
Recovery of petroleum contained in geologic formations is often hindered by the presence of paraffinic or asphaltenic solids. During recovery or processing of crude petroleum high molecular weight paraffinic or asphaltenic compounds can precipitate as waxy or tarry solids. These solids tend to fill the pores of the petroleum reservoir rock, and additionally clog well-casings, tubing, and other auxiliary equipment used in petroleum recovery or processing. Wells plugged by paraffins or asphaltenes have a diminished production rate, and extreme cases of deposition can lead to the total loss of well production.
Although several methods of removing deposited solids have been developed, including mechanical scraping, treatment with hot oil, or treatment with aqueous surfactants, the use of organic solvents to remove paraffinic and asphaltenic deposits is often preferred because of their efficacy and economy of use. Although many industrial solvents have been evaluated for removal of paraffinic and asphaltenic deposits, considerations of cost, safety, and efficiency of deposit dissolution has resulted in only a few solvent compositions being used commercially. Among the solvents that have been tried to remove paraffin deposits are straight chain hydrocarbons, such as kerosene, diesel oil, naphtha, or even light crude oil. These compositions have shown some solvent functionality but their efficacy is highly dependent on the type of petroleum deposit. Asphaltenes are most efficiently removed by aromatic solvents such as benzene, toluene, or xylene, which themselves exhibit a much reduced capacity to dissolve paraffinic hydrocarbons. Because their high volatility, low flash points, and high carcinogenic potential collectively create a substantial human and environmental hazard, commercial use of aromatic solvents is limited.
Solvent additives are known to effect the dissolution characteristics of solvent compositions. For example, the addition of small amounts of additives such as carbon disulphide, n-butylamine, dicyclopentadiene, or xylene, to selected solvents has been shown to improve their effectiveness as solvent compositions used for oil well treatment. However, many art-recognized solvent additive compositions can be unsafe in addition to having the substantial drawbacks of expense and varying utility in removing asphaltene or paraffin deposits from oil wells.
It is therefore an object of the present invention to provide a safe, inexpensive, and efficient method and a composition for dissolution of asphaltenic and paraffinic deposits derived from petroleum.
It is a further object of this invention to provide a method and a composition for removal of solid deposits from petroleum recovery and processing equipment.
It is yet another object of this invention to provide a method and a composition for removing petroleum derived solids deposited in the pore spaces of a petroleum reservoir rock.
Those objects and others are accomplished in accordance with one embodiment of this invention comprising a mixture of an aliphatic hydrocarbon petroleum distillate and at least 3% by volume of an alkyl phenol. For the purposes of the present invention, aliphatic hydrocarbon petroleum distillates are defined to include small fractions of aromatic and cyclic hydrocarbons in addition to the predominant straight chain alkane components. Preferably, the alkyl phenol is utilized in the composition of the present invention in an amount of about 3% to about 15% by liquid volume. In one preferred embodiment about 4% to about 7%, more preferably about 5% by volume of alkyl phenol is utilized in admixture with an aliphatic hydrocarbon petroleum distillate. While cresol is a preferred alkyl phenol for use in the composition of this invention, cresylic acid, an industrial grade fraction containing C.sub.9 -phenols, can be used in admixture with aliphatic hydrocarbon distillates in amounts ranging between about 3% and 15% by volume of the mixture. As defined herein and with reference to the Condensed Chemical Dictionary, 9th Edition, cresylic acid is derived from petroleum and consists of an industrial cut of phenolic material boiling above the cresol range. A typical commercial cut contains less than 1% cresol. Cresylic acid is predominantly composed of xylenols and C.sub.9 phenols.
This invention is also directed to a composition comprising a mixture of kerosene and an alkyl phenol for dissolution of paraffinic and asphaltenic deposits. Preferably, the alkyl phenol is a cresol, present in the composition at about 1% to about 15%, more preferably about 3% to about 7%, by liquid volume. In a most preferred embodiment of this invention a composition if provided which comprises 5% cresol by volume in admixture with kerosene.